Safety syringes are used in healthcare to prevent needlestick injuries, that is, injuries to health workers and other persons that result from being stabbed by needles that have been used to inject patients. In many cases, needlestick injuries are minor, but in cases where the needle concerned is infected, for example, with the AIDS virus, the injuries can have serious implications.
A further concern relating to the use of needles in the healthcare field is re-use. In order to prevent the spread of disease, sharing of needles should be prevented.
One way of preventing needlestick injuries and re-use of needles is to ensure that needles are unusable following use.
An example of a safety syringe that prevents re-use of the syringe needle is disclosed in EP 0 636 381B. That syringe provides for engagement of a needle hub, which carries a needle, by a plunger that is used to expel a substance from the syringe, following the expulsion of that substance. Once the plunger has engaged the needle hub, it can be manually retracted into the syringe, bringing the needle hub and attached needle with it. A stop is located in the syringe to prevent removal of the plunger from the syringe, so that the needle hub and needle remain inside the main body of the syringe, so as to avoid injury.
One disadvantage of the syringe disclosed in EP 0 636 381B is that the plunger and attached needle hub need to be retracted into the syringe by the healthcare worker, which means that human error could result in the needle hub not being retracted at all, for example, because the healthcare worker omitted to complete the retraction step. For this reason, automatic retraction of the needle hub into the syringe is desirable.
An automatic retraction system for syringes is described in U.S. Pat. No. 6,572,584. That system incorporates a pre-stressed compression spring in the region of the needle hub. When the compression spring is allowed to relax following injection of the substance carried by the syringe, the needle hub is forced into the syringe by the restoring force of the spring, so that the needle is safely disposed of. Although the spring in the region of the needle hub is effective in automatically retracting the needle hub into the syringe, the syringe has a complex construction, which means that it is costly to produce.